Instead of having the railings built into the stair tool, railings should instead be a separate object that can be associated with stair objects.
Railings are something that can go beyond a stair and are found in many places other than stairs, so by having railings built into the stair tool as well as a separate tool for railings, Vectorworks is doubling up on development effort. These tools should be separated out, so that Vectorworks can focus on making each of them excellent at what they need to do and so that use users can focus on modelling separate elements with less limitations and less variables to worry about.
The more I model with Vectorworks the more I want to break things down into separate elements so that there are less variables and connections to think about. When too many things are bundled up into one tool it creates limitations that don't exist in the real world. Fine if you're modelling a square box. Not fine otherwise.
Breaking slabs and roofs down into internal finishes, structure and external finishes is a good example of this. And it makes even more sense to me to do this with railings and stairs.